A large number of measurements are conducted in conjunction with industrial production processes, in conjunction with the manufacture as well as with the quality control of an object. Traditionally, these measurements have been conducted by means of a coordinate measuring machine. In this type of system, the measuring system measures the desired points in the object by mechanical probing. Advantages of the traditional system include high accuracy and number of applications. The weakness of the measuring system resides in its slowness. Furthermore, such systems do not detect all deviations in the measured object. For example, in the case of measuring a hole made in the object, the hole is measured by probing a desired number of points on the circumference of the hole. If the object contains a defective section, it is detected only when the probe of the measuring device comes into contact with the defective section.
To solve this problem, different kinds of machine vision systems which perceive the object as a whole and are able to detect any deviating forms in the object have been developed. Particularly preferred machine vision systems are those in which the cameras and the indicating device of the measuring system are calibrated to the same measurement space. Preferably, this measurement space is three-dimensional. One such system is presented for example in patent publication WO02086418.
Use of the above-mentioned systems for quality control is particularly useful in the production-line industry where very large quantities of objects are being manufactured. In this kind of industry, the staff is not able to check each manufactured object. A similar need is also present in the industries which use these objects in their own products. For example, in the automobile industry, it is very important that the manufactured products are safe for the users. Consequently, the quality should be excellent. If a component is suspected as defective, this may lead to a check campaign in which vehicles are called for service in order to check certain parts. This is required specifically in cases where the part may suddenly break and cause a severe danger. Typically, such campaign is very expensive because it is not possible to limit the number of the defective parts precisely, but instead a larger number of possibly defective parts are checked for safety precautions than what is the actual number of the defective parts that were manufactured. Further, it is possible that the defect presents itself in such portion of the object that has not been measured in the production stage, for example because it has not been possible to conduct the measurement. For example, measuring the quality of welded seams by means of a machine vision system is known to be a difficult task.
Due to the above-mentioned features, there is an obvious demand for improved measuring systems which are able to solve the problems of the systems according to the known technology and thereby improve the reliability of the measurement results and utilization of the measurement data.